As described in previous reports, a hemagglutination inhibition test suitable for the diagnosis of pregnancy in macaques has been developed in this laboratory. The Subhuman Primate Pregnancy Test kit distributed under the aegis of the Contraceptive Development Branch, Center for Population Research, NICHD has been sent to primate facilities all over the world. To date, more than 700 kits have been delivered, sufficient for 35,000 pregnancy tests. In order to realize the full potential of this kit, we have undertaken a series of studies to determine the interval for most reliable detection of urinary chorionic gonadotropin in macaques, baboons, marmosets, chimpanzees, and orangutans and squirrel monkeys. The first 5 of these are now complete. BIBLIOGRAPHIC REFERENCES: Hodgen, G.D., Wolfe, L.G. Ogden, J.D., Adams, M.R., Descalzi, C.C. and Hildebrand, D.F.: Diagnosis of Pregnancy in Marmosets: Hemagglutination Inhibition Test and Radioimmunoassay for Urinary Chorionic Gonadotropin. Lab. Anim. Sci. 26: 224-229, 1976. Hodgen, G.D., Turner, C.K., Smith, E.E., and Bush, R.M.: Pregnancy Diagnosis in the Orangutan (Pongo Pygmaeus) Using the Subhuman Primate Pregnancy Test kit. Lab. Anim. Sci. 27: 99-101, 1977.